Interpretive Summary: Developing alternative approaches to disease control is a critical objective of NP-303, Plant Diseases, due to consumer demands to lower exposure to chemicals, and reduces the impact of agriculture on the environment. USDA-ARS has identified several species of yeasts that can be used as biocontrol agents against postharvest diseases of fruit. Use of these biocontrol agents, however, is limited due to their variable performance. Therefore, there is a need to find strategies that will increase the efficacy of these bicontrol agents and allow them to perform more reliably under variable and often adverse environmental conditions. The use of heat treatments to induce resistance in fruit and to increase the tolerance of yeast to adverse conditions has been explored. In the present study, the effect of heat treatments on the spores of the fungus (Botrytis cinerea) that causes gray mold in a wide variety of fruit and ornamental species was examined. Additionally, the use of heat treatments on harvested pears was evaluated as a method to inhibit gray mold. We demonstrated that increasing exposure of the fungal spores to high temperatures inhibited both germination and subsequent growth. The heat treatments resulted in high levels of oxidative stress in the fungal spores which in turn resulted in partial degradation of proteins and membrane lipids. Heat treatment of pear fruit was also very effective at reducing postharvest gray mold infections in wounded fruit. The use of heat treatments represents a useful strategy for improving the efficacy of postharvest biocontrol agents. Further studies on fruit physiology are required to ensure that the prescribed heat treatments do not adversely affect fruit quality or storage.

Technical Abstract:
The inhibitory effect of a heat treatment (HT) on Botrytis cinerea, a major postharvest fungal pathogen, and the possible mode of action were investigated. Spore germination and germ tube elongation of B. cinerea were both increasingly and significantly inhibited by a HT (43 degrees C) for 10, 20 or 30 min. HT-induced gene expression of NADPH oxidase A resulted in the intracellular accumulation of reactive oxygen species (ROS). HT-treated B. cinerea spores exhibited higher levels of oxidative damage to proteins and lipids, compared to the non-HT control. These findings indicate that HT resulted in oxidative damage which then played a crucial role in the inhibitory effect on B. cinerea. In the current study, HT was effective in controlling gray mold caused by B. cinerea in pear fruits. Understanding the mode of action by which HT inhibits fungal pathogens will help in the application of HT for management of postharvest fungal diseases of fruits and vegetables.